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Webhook Retry Best Practices

If you're like me, you've probably spent a fair share of your developer life dealing with webhooks. Webhooks are truly fantastic and a vital part of any software integration toolkit. Yet, handling webhook retries can sometimes feel like threading a needle in the dark. Thankfully, there are best practices to make it a smooth sail. In this post, I will talk about those practices and how we, at Svix, handle retries in our Webhooks as a Service.

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Understanding the Problem

Before we jump into the solution, it's crucial we understand the problem. Sometimes, your service might fail to deliver a webhook due to temporary issues like network glitches, or your customer's server being overwhelmed or outright down. It would be a shame for a minor hiccup to cause permanent data loss, wouldn't it?

That's where retries come into the picture to ensure that these minor obstacles don't impact service delivery. But if not handled correctly, retries can result in complications such as duplicate events, sequence chaos, or processing delays.

Best Practice #1: Exponential Backoff

One proven strategy to handle retries is exponential backoff. If your initial attempt to send a webhook fails, you don't want to keep hammering the server incessantly. Instead, you wait for a brief moment and then try again. If it fails the second time, you wait a bit longer, and the cycle continues.

This waiting period should grow exponentially, but you need a cap on it so that you're not waiting for days before making the next attempt. This algorithm helps avoid overwhelming your customer's server, especially if it's struggling to recover from an outage.

Best Practice #2: Jitter

Just using exponential backoff, however, might lead to a thundering herd problem where a lot of webhook events are retried simultaneously. This could potentially bring down a service that just recovered. That's where "jitter" comes in.

Jitter is basically a fancy term for adding a bit of randomness to your retry intervals to spread out the load. It prevents all of those webhooks from hammering the server at the same moment.

Best Practice #3: Dead Letter Queue

There comes a time when you have to accept that a webhook is just not getting through. After a certain number of retry attempts, it's probably best to move the event to a Dead Letter Queue.

This queue stores the events that couldn't be delivered, so you can inspect them later. Perhaps there was an issue with the payload, or the receiving server's been down for a prolonged period. Regardless, it's good to know when to stop trying and start investigating.

Best Practice #4: Allow Customization

Every system is unique, and what's right for one might not be right for another. Hence, it's a good practice to let your customers customize their webhook retry policy. They may want to set their own thresholds for retries or customize the backoff algorithm, and that's okay. More power to them!

Best Practice #5: Documentation

One thing we see get overlooked a lot with retries is documentation. Some providers don't mention them at all (do they even retry?). Others will mention them in passing ("We retry 5 times").

What users really need is a fully detailed explanation of your retry policies. What is the exact retry schedule? What response codes trigger retries vs don't?

Make sure your docs give a full explanation of how retries work for your service so your users can rely on it.

How Svix Handles Retries

At Svix, we've built our retry system keeping these best practices in mind. We use an exponential backoff algorithm with jitter to prevent overwhelming servers and to avoid the thundering herd problem.

If, after multiple attempts, we're unable to deliver a webhook, we move it to our Dead Letter Queue, providing you with the opportunity to inspect and troubleshoot the issue.

Security and reliability are our top priorities. Therefore, our webhook handling is robust and flexible enough to meet the varying needs of our clients, allowing customization to fit their unique situations.

Wrapping Up

Handling webhook retries effectively is an art and science. It's a delicate balance between ensuring delivery and not overwhelming the receiving system. By following these best practices and fine-tuning them to your specific needs, you can create a robust and reliable system, just like we strive to do at Svix.